Molecular beam epitaxy (MBE) is a term used to denote the epitaxial growth of semiconductor films by a process involving the reaction of one or more thermal molecular beams with a crystalline surface under ultra-high vacuum conditions. Use of shutter mechanisms and relatively slow growth rates (e.g., 1 .mu.m/hr.) allow rapid changing of beam species and growth of layers as thin as a monolayer.
In addition, since electrically active impurities are added to the growing film by means of separate beams, the doping profile normal to the surface can be varied and controlled with a spatial resolution difficult to achieve by more conventional, faster growth techniques such as CVD and LPE.
MBE has been used to fabricate films of a variety of material from elemental materials such as Si to Group III-V compounds as well as Group II-VI and Group IV-VI materials. Silicon MBE is related to Group III-V MBE in terms of the equipment and processes used for epitaxial growth. It differs profoundly, however, in other aspects such as growth temperature, defect structures, device applications, and in the type and quality of competing epitaxial growth techniques.
In most silicon MBE arrangements, silicon growth substrate heaters are relatively simple structures employing direct ohmic heating of the substrate. The growth substrate in this type of arrangement is clamped at opposite ends and a voltage is applied thereto. To achieve uniform heating of the substrate, growth substrate geometries have been modified to be rectangular. Also the growth substrate is often heavily doped to minimize the voltage required for initial heating. In practice, however, uniform heating does not occur because each clamp holding the growth substrate tends to act as a heat sink thereby cooling each end of the growth substrate. Moreover, a non-uniform current results within the substrate because electrical contact is made at only one location for each clamp.
It is an object of the present invention to provide reproducible, uniform heating of silicon growth substrates, regardless of geometry, to temperatures required for epitaxial growth in an ultra-high vacuum environment.
It is a further object of the present invention to provide the appropriate temperature environment which will yield high quality, low defect density epitaxially grown material suitable for subsequent integrated circuit fabrication.